Measuring based on an oscillating sensor of angular velocity has proved to have a simple principle and to provide a reliable way of measuring angular velocity. The operating principle most generally used in oscillating sensors of angular velocity is the so called tuning fork principle.
In an oscillating sensor of angular velocity, a certain known primary motion is generated and maintained in the sensor. On the other hand, the desired motion to be measured by means of the sensor is detected as a deviation in the primary motion. In the tuning fork principle, the primary motion is the opposite phase oscillation of two vibrating linear resonators.
An external angular velocity affecting the sensor in a direction perpendicular to the direction of motion of the resonators induces Coriolis forces on the masses in opposite directions. The Coriolis force, proportional to the angular velocity, is detected either directly from the masses, or the masses are connected to the same rotation shaft, and then the detection motion is an angular oscillation in the direction of the angular velocity axis.
Resistance to vibration and impact are central features required of sensors of angular velocity. Particularly in certain demanding applications, like, for example, electronic stability programs in the automotive industry, these requirements are extremely tight. Even a hard blow, like, for example, the external impact caused by a stone, or the vibration caused by a car audio player, should not affect the output of the sensor of angular velocity.
In measuring according to the tuning fork principle, the detection motion is angular oscillation or differential linear oscillation, and thus, any external linear acceleration will not link to the detecting resonator in an ideal structure. Unavoidably, however, angular accelerations also to the axis of detection of the sensor of angular velocity will always be generated from impacts and vibrations, due to vibration in the material and the support. Thus, the motion of the detecting resonator will unavoidably be disturbed, and this causes deviations in the output signal of the sensor of angular velocity, particularly when the frequency of the interference is close to the operating frequency of the sensor.
Sensors of angular velocity according to prior art have also been developed, in which both the primary motion and the detection motion are angular oscillations. One such prior art solution for a sensor of angular velocity is described in e.g. U.S. Pat. No. 6,349,597. The primary motion in the solution for a sensor of angular velocity described in the U.S. patent is implemented as an angular oscillation about an axis z occurring in the plane of the disk. The angular velocity detection motion is correspondingly measured as an inclination of the disk in relation to the plane z. In the presented solution the moment caused by the angular velocity is, in addition to being proportional to the mass of the oscillating structure, proportional to the square of the length of the mass in the direction of the axis of angular velocity.
The prior art solution described above, however, exhibits almost the same degree of sensitivity to external mechanical interference as structures based on the tuning fork principle. Only the primary motion, being an angular oscillation, is less sensitive to linear accelerations, but the primary motion is, anyhow, clearly less sensitive to external forces than the detection motion.
The measuring principles of micro-mechanical sensors of angular velocity generally known at the present time are not the best possible ones in view of sensitivity to vibration. Thus, an object of the invention is to provide a structure for an oscillating sensor of angular velocity, which is appreciably less sensitive to the linkage of mechanical interference compared with solutions according to prior art.